Epithelial cells form membrane sheets which serve as a interface between tissue compartments. The transport of specific macromolecules across this barrier is critical to the proper functioning of most tissues. In order to accomplish specific and directional transport, the plasma membrane of epithelial cells is divided into two subdomains; apical facing the exterior environment or the tissue lumen, and basolateral facing other epithelial cells and the extracellular matrix. These domains maintain distinct protein compositions, and trafficking at each of these domains is uniquely regulated. Regulation of vesicle transport is carried out by small GTPases of the Ras superfamily, including ADP-ribosylation factors (ARFs). One ARF protein, ARF6, functions in the endocytic pathway in non-polarized cells and seems likely to regulate endocytosis at the apical pole of polarized epithelial cells. The overall aim of this proposal is to define the role of ARF6 and a potential downstream effector, phospholipase D, in endocytosis at the apical pole of polarized epithelial cells.